Calculate the internal energy change in each of the following cases :
(i) A system absorbs 5 kJ of heat and does 1 kJ of work.
(ii) 5 kJ of work is done on the system and 1 kJ of heat is given out by the system.

Explanation

(i) Here q + 5 kJ and w = - 1 kJ
`therefore` According to first law of thermodynamics, `Delta E=q+w=5+(-1)=4kJ`
(ii) Here w = + 5kJ and q = - 1kJ
`therefore` According to first law of thermodynamic `Delta E=q+w=-1+(+5)=4 kJ`
i.e. the internal energy of the system increases by 4 by in each case.